The present invention relates, in general, to etching a substrate, and more particularly, to etching a dielectric material over a semiconductor material.
Wet etching is widely used in semiconductor processing for removing dielectric material, e.g., oxide, from a semiconductor wafer. In one wet etching process, an etchant such as a six to one buffered oxide etchant (6:1 BOE), which consists of six parts of ammonia fluoride and one part of hydrogen fluoride, is used to etch an oxide layer, such as a phosphorus doped silicate glass (PSG) layer, on a semiconductor wafer. The process starts with dipping the semiconductor wafer into a surfactant. The semiconductor wafer is then submerged into a recirculating bath of the etchant to etch the sacrificial oxide. After etching, the semiconductor wafer is rinsed in deionized water and then dried in an isopropyl alcohol vapor. In some applications, e.g., in sensor applications, the semiconductor wafer is submerged in a hydrogen peroxide solution after it is rinsed in the deionized water, followed by a second deionized water rinse before being dried in the isopropyl alcohol vapor.
If the semiconductor wafer includes a conductive structure such as a polycrystalline silicon structure, the polycrystalline silicon structure is exposed to the etchant after the sacrificial oxide is etched away. The etchant etches the polycrystalline silicon, wherein the extent of the etching is dependent on the composition and temperature of the etchant as well as the duration of the etching process. If the polycrystalline silicon is structured as thin conductive lines electrically connecting different components on the semiconductor wafer, the etching process can create open circuits in some areas on the wafer. The etching process also creates reliability problems when a polycrystalline silicon line is etched to a very thin line because a thin line cannot carry the current required for the circuit in the semiconductor wafer to perform properly.
Accordingly, it would be advantageous to have a process for etching a dielectric material over a semiconductor wafer that does not damage a conductive structure on the wafer. It would be of further advantage for the etching process to be simple and easily integrated into an existing etching process.